The Syrian Observatory said the death toll was likely to rise because bodies were still being pulled from the rubble, adding that "it is extremely difficult to count the dead because most of the bodies have been immolated."

The Local Coordination Committees, a grassroots network of activists, estimated that at least 50 people were killed and dozens of others wounded.

The attack came on the same day that a top UN official said more than 60,000 people have been killed in Syria since the uprising against President Bashar al-Assad's regime broke out in March 2011.

Navi Pillay, the UN High Commissioner for Human Rights, said that an exhaustive analysis carried out by data specialists showed that 59,648 people had died through the end of November.

"Given there has been no let-up in the conflict since the end of November, we can assume that more than 60,000 people have been killed by the beginning of 2013," Ms Pillay said in a statement.